Magnetron



April 14, 1953 5 MlLLMAN 2,635,210

MAGNETRON Filed March 1, i946 'l'l'l'l'l'l 0.0. SOURCE 0R MODULATORFIG.5. FIG.5A

IN V EN TOR.

SIDNEY MILLMAN B Y b J WMM ,9- H 1 Patented Apr. 14, 1953 MAGNETRONSidney Millman, Brooklyn, N. Y., assignor to the United States ofAmerica. as represented by the Secretary of War Application March 1,1946, Serial No. 651,318

6 Claims. 1 This invention relates to ultra-high frequency generators ofmagnetron type in which ultra-high frequency oscillations are generatedby a bunched plurality of resonators set into oscillation by highvelocity electrons moving along curvilinear, orbital paths, these pathsbeing followed by the electrons because of the joint action of theelectric, magnetic and radio frequency electromagnetic fields.

It is an object of this invention to provide an improved ultra-highfrequency magnetron with an anode structure having higher efficiencyobtained by an increase in the L/C ratio of each cavity.

t is an additional object of this invention to provide simplifiedanodestructure and methods of manufacturing anodes for ultra-highfrequency magnetrons.

The invention discloses an improved anode structure and the method ofits manufacture which facilitates their production from a mechanicalpoint of view. Moreover, it also results in the productionof an anodewith superior electrical characteristics including higher circuiteniciency. The smaller losses are obtained by increasing the inductanceL of the oscillating circuit accompanied by a decrease in itscapacitance.

These and other features of the invention will be more clearlyunderstood from the following detailed description and the accompanyingdrawings in which:

Figure l is a plan view of an anode block with anode vanes indicated bydotted lines,

Figure 2 is a side, cross-sectional view taken along line 22 of theanode block illustrated in Fig. l,

Figure 3 is a perspective view of a jig used in assembling the anodeblock and the vanes, the latter two being illustrated in Fig. 3 insection,

Figure 4 is a perspective view of an anode vane,

Figures 5 and 5-A are enlarged plan and side views of a portion of theanode ring and several vanes;

Figure 6 is a plan view of a magnetron withthe top cover of the anoderemoved;

Figure 7 is a vertical, cross-sectional view,

taken along line l-|, of the magnetron illustrated in Fig. 6.

.in Fig. 2. Bore is provided in the block for facilitating thesubsequent assembly of the anode block illustrated in Figs. 1 and 2 is afourteenvane block. The upper portion of the block as seen in Fig. 1 isprovided with fourteen radial slots l2 which are cut in the block on amilling machine. The center lines of the slots i2 emanate from center 14of the cylindrical block. and the sides of the slots are parallel totheir respective center lines. The side View of two slots lzaand l2b areillustrated in Fig. 2. The slot axial length 21 extends beyond the anodeportion IQ of the block. The milled slots l2 in the anode block are usedfor holding the anode vanes, one of which is illustrated in Fig. l. Thevanes are made of copper and represent rectangular plates it of uniformthickness, 52. Edge 31 of the platerepresents the inner surface or apole-piece of the anode resonator facing the cathode. The height 55 ofthe plate I8 may be either larger or equal to the depth 34 of the slotsdepending upon whether the upper and lower portions of the finishedanode structure are leveled, upon the completion of the anode assembly,on a milling machine as will be described later. After completion of themilling operation of the anode block, rectangular plates l8 are insertedinto the slots in the following manner: block In is placed on anassembling jig l9 illustrated in Fig. 3. The jig consists of acylindrical base 20 and two cylindrical pedestals 22 and 24. Thediameter of pedestal 24 is made equal to the innerdiameter 58 of theassembled anode. The diameter of pedestal 22 is substantially equal tothe inner diameter of bore I l in the anode block so that the blockforms a tight sliding fit over the pedestal 22, and resting on the topsurface of pedestal 20. The height of pedestal 22 isequal to thenon-slotted height 26 of the anode The anode block in proper made byplacing vanes in this block. The so block. Therefore, when block it) isplaced on the jig, the flat bottom surfaces 2? of the slots i2 are onthe same level with the flat circular area 28 of the jig. After theanode block has been mounted on the jig, in a manner illustrated in Fig.3, the

anode vanes l8, whichform a tight sliding fit with the anode slots 12,are inserted into the slots so that the inner tips of the vanes restagainst the cylindrical pedestal 24. The latter pedestal thus insuresproper. centering of the vanes within the anode block. The circularsurface 28 of the jig and the bottom surfaces 21 of the slots providerest surfaces which align the lower edges 350i the vanes so that theinner tips Si of the vanes form a true cylindrical locus defining theouter boundary of the discharge space between the cathode and the anodeof the magnetron, After the insertion and alignment of the anode vanesinthe anode block the latter is removed from the jig and placed into ahydrogen bottle for soldering the vanes to the block. A high meltingpoint silvercopper may be used for completing this soldering operation.It is advisable that the soldering operation is performed in a hydrogenbottle to avoid any oxidation of the anode structure. Upon thecompletion of the soldering operation, the anode block is taken out ofthe hydrogen furnace, allowed to cool, and then placed on the millingmachine. Here the excess portion of the copper block, represented byring 32 in Fig. 2, is cut oil to a depth represented by a dimensionalarrow'33 in Fig. 2. The milling operation also cuts off the bottomportions of the vane plates 18 which, as it will be remembered,projected beyond the depth of the anode portion proper I6. The sameleveling operation is performed in the upper surface of th anode. Thiscompletes the manufacturing steps of the anode structure; a portion ofthe completed structure is illustrated on an enlarged scale in Figs. 5'and5-A.

The radial length 5! of the anode vane is determined by the wave lengthof the magnetron,

while its thickness 52 and opening 53 of the anode cavity are controlledby the running wave oscillations typical of this type of anodestructure. If t is the vane thickness and a. is the cavity opening, theratio of t/a should be equal at least to unity; the efliciency improveswith the increase in this ratio; this ratio may be as high as 2; forshort wave magnetrons (12 cms.) the optimum value of this ratio wasfound to be in the order of 1.8.

Referring now to Figs. 6 and '7, after completion of the assembly andfinishing of the anode block i0 it is inserted into a copper shell 666.The anode forms a tight sliding fit with the shell and upon theinsertion of the anode into the shell, with the aid of proper jigs, theshell and the anode are soldered together by means of RT solder (16%silver, copper, 15% zinc) which has a lower melting point than the BTsolder previously used for soldering the anode vanes to the anode block.Anode block 666 is made of oxygen-free, high-conductivity copper whichis provided with recesses Bill and 602 for holding tightly fittingbronze or copper shell-covers 694 and 606. These covers, upon thecompletion of the assembly of the magnetron, are soldered to the anodeshell with one of the above-mentioned solders to make an air-tight jointwith the shell.

The upper end space 669 of the magnetron is used for inserting thecoupling loop 6H] and a concentric line 612. The line includes atapered, copper sleeve 6M, forming an airtight joint with the shell,metallic eyelet M6 in a glass seal 618 with the center conductor 620 ofthe line projecting through the glass seal. Conductor 626 terminates inthe coupling loop 616 which is placed directly above one of theresonating cavities of the anode as illustrated more clearly in Fig. 6.One end of the loop is connected to the inner end of the copper sleeve614 in the usual and this coaxial relationship. is maintained by glassseals 628 and 629 respectively. The cathode itself consists of a nickelcylinder 630 coated with electron-emitting oxide or a mixture of severaloxides. The cathode is provided with two hats for shielding thedischarge space from the end spaces. Within the nickel cylinder 630 ofthe cathode is a heater coil, not visible in any of the figures, whichis connected to the cathode conductors 621 and 622 by jumpers 6'3! and632, which complete the circuit of the cathode. While conventionalradial type of cathode structure has been illustrated in'the figures,itis to be understood that the package-type or soldering iron type ofcathode structures could be used for accomplishing the desired result.Moreover, when the radial type of the cathode structure is used, it mayhave the provisions for maintaining properly centered position of thecathode with respect to the anode at the operating temperatures of themagnetron, such as those described in the application for patent ofPolykarp Kusch, Serial No. 604,071, filed July 9, 1945, entitled CoaxialCathode Lead for Magnetron. Two polepieces 633 and 634 are placeddirectly on the plates 604 and 666 of the shell, these pole-pieces beingdirectly connected to the permanant magnets not illustrated in thefigures. The magnets furnish the necessary magnetic field for thedischarge space of the magnetron. I

From the foregoing it will be apparent to those skilled in the art thatI have provided an improved magnetron and the method of manufacturingthe latter. The disclosed method simplifies the manufacturing techniquesof the anodes. Besides facilitating the manufacturing techniques, I havealso produced a magnetron having higher electrical eficiency and higherpower capacity. The higher efficiency is obtained because of theinherently lower losses in the disclosed anode structure. The higherpower capacity is obtained because of the higher circuit efficiency.

While the invention has been described with reference to severalparticular embodiments, it will be understood that various modificationsof the apparatus shown may be made within the scope of the followingclaims.

I claim:

1. An anode for an ultra-high frequency magnetron comprising 'aplurality of conductive wedge-shaped elements mounted in a circle andspaced from one another and a like plurality of conductive vanesdisposed between and connected to said elements forming a compositering,

said vanes extending from the inner surface of said ring and formingwith the inner surfaces of said elements cavity resonators ofsector-shaped cross-sections.

2. An anode as defined in claim 1 in which the ratio of the thickness ofsaid vanes to the air-gap between the inner ends of said vanes isbetween unity. and two.

3. An anode for an ultra-high frequencymagnetron comprising a pluralityof conductive wedge-shaped elements mounted in a circle and uniformlyspaced from one another and a like plurality of rectangular metallicvanes radially disposed with respect to said, circle between saidwedge-shaped elements and electrically connected to saidelements forminga composite said anode, said block being provided with a plurality ofradial slots extending radially therethrough and axially at least alongthe entire length of said first bore.

5. An anode block for a magnetron anode having a plurality of cavityresonators therein, said block being provided with first and secondcylindrical bores coaxially aligned, the radius of said first bore beingsmaller than that of said second bore and being equal to the outerradius of the cavity resonators of said anode, said block being providedwith a plurality of radial slots extending radially therethrough andaxially at least 7 along the entire length of said first bore, saidslots being dimensioned for holding vanes which form the cavityresonators of said anode.

6. A magnetron anode comprising, an anode block provided with first andsecond coaxially aligned cylindrical bores, the radius 01 said firstbore being smaller than that of said second bore, said block beingprovided with a plurality of radial slots extending axially along theentire length of said first bore, and an equal plurality of vanesdisposed respectively within said slots and extending the entire axialand radial lengths of said slots into the center of said block, thespaces between said vanes forming a plurality of cavity resonatorsdisposed within and extending the entire length of said first bore.

SIDNEY MILLMAN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,063,342 Samuel Dec. 8, 1936 2,247,077 Blewett et a1. June24, 1941 2,305,781 Helbig Dec. 22, 1942 2,408,238 Spencer Sept. 24, 19462,410,396 Spencer Oct. 29, 1946 2,416,899 Brown Mar. 4, 1947 2,520,955Okress et al. Sept. 5, 1950 2,542,966 Randall et al. Feb. 20, 1951FOREIGN PATENTS Number Country Date 509,102 Great Britain July 11, 1939

